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There was probably better chances of approval if you wouldn't have added invitation. "Invitation" has no real merit on a TRV application given the applicants profile.

Also, "father's overseas employment" is another red flag as it shows applicant has no immediate family in home country. Age is not making it favourable either.

Basically need strong financials and proof of being established in home country for a successful tourist visa.
Strong financials ?? How much of bank balance